Waiting for the response to come by subscribing in Angular

Question

Waiting for the response to come by subscribing in Angular

I am encountering an issue while trying to subscribe to an Observable and assign data from the response. The problem is that my code does not wait for the response before executing the console.log(this.newIds) line, resulting in an empty value being logged. How can I ensure that my code waits for the response from the backend before proceeding?

 this.repository.getById(Ids).subscribe((response) => {
      console.log(response);
      this.newIds = response.map((id) => {
        return id;
      });
    });
    console.log(this.newIds);

javascript angular typescript asynchronous

Answer 1

Answer №1

When you place the code inside the subscribe callback, it will only run after receiving a response from the back-end. Any code outside of this function will be executed immediately.

this.repository.getById(Ids).subscribe((response) => {
          //Code will execute when back-end responds
          console.log(response);
          this.newIds = response.map((id) => {
            return id;
          });
          console.log(this.newIds);
        });
//Code will execute without waiting

For more information, visit: https://angular.io/guide/observables#creating-observables

Answer 2

When you place the code inside the subscribe callback, it will only run after receiving a response from the back-end. Any code outside of this function will be executed immediately.

this.repository.getById(Ids).subscribe((response) => {
          //Code will execute when back-end responds
          console.log(response);
          this.newIds = response.map((id) => {
            return id;
          });
          console.log(this.newIds);
        });
//Code will execute without waiting

For more information, visit: https://angular.io/guide/observables#creating-observables

Answer 3

Answer №2

This situation is considered normal as the console.log(this.newIds); statement falls outside of the subscription block. To rectify this, simply move it inside the .subscribe() method like so:

 this.repository.getById(Ids).subscribe((response) => {
          console.log(response);
          this.newIds = response.map((id) => {
            return id;
          });
          console.log(this.newIds);
    });

If you need to access this.newIds outside of the subscription and immediately after receiving the observer's result, you can utilize RxJs .toPromise() to convert it into a promise and switch the method to async:

async callerFn(){

    const response = await this.repository.getById(Ids).toPromise();
  
    this.newIds = response.map((id) => {
        return id;
    });
    console.log(this.newIds);
    // Use your property here

 }

Answer 4

This situation is considered normal as the console.log(this.newIds); statement falls outside of the subscription block. To rectify this, simply move it inside the .subscribe() method like so:

 this.repository.getById(Ids).subscribe((response) => {
          console.log(response);
          this.newIds = response.map((id) => {
            return id;
          });
          console.log(this.newIds);
    });

If you need to access this.newIds outside of the subscription and immediately after receiving the observer's result, you can utilize RxJs .toPromise() to convert it into a promise and switch the method to async:

async callerFn(){

    const response = await this.repository.getById(Ids).toPromise();
  
    this.newIds = response.map((id) => {
        return id;
    });
    console.log(this.newIds);
    // Use your property here

 }

Answer 5

Answer №3

Absolutely, the way JavaScript interprets code is line-by-line execution, meaning it doesn't wait for other processes to finish. This explains why the last console log will return undefined. However, if you place the console logs inside the subscriber function, you'll receive the expected output as the subscriber waits for the response before binding it with this.newIds.

 this.repository.getById(Ids).subscribe((response) => {
      console.log(response);
      this.newIds = response.map((id) => {
        return id;
      });
     console.log(this.newIds);
    });

If you're interested in learning more about observable subscribe functionality, I recommend checking out this resource:

Additionally, if you need to access newIds outside of the subscriber scope, consider using promises with async await. Here's a sample implementation:

 async getAsyncData() {
    this.asyncResult = await this.httpClient.get<Employee>(this.url).toPromise();
    console.log('No issues, I will wait until promise is resolved..');
  }

Answer 6

Absolutely, the way JavaScript interprets code is line-by-line execution, meaning it doesn't wait for other processes to finish. This explains why the last console log will return undefined. However, if you place the console logs inside the subscriber function, you'll receive the expected output as the subscriber waits for the response before binding it with this.newIds.

 this.repository.getById(Ids).subscribe((response) => {
      console.log(response);
      this.newIds = response.map((id) => {
        return id;
      });
     console.log(this.newIds);
    });

If you're interested in learning more about observable subscribe functionality, I recommend checking out this resource:

Additionally, if you need to access newIds outside of the subscriber scope, consider using promises with async await. Here's a sample implementation:

 async getAsyncData() {
    this.asyncResult = await this.httpClient.get<Employee>(this.url).toPromise();
    console.log('No issues, I will wait until promise is resolved..');
  }

Answer 7

Answer №4

If you want to achieve this functionality, follow the steps below:

In your component file, add the following code snippet:

newIds: Observable<any> ➜ of(this.id).pipe(
  concatMap((id) ➜
    this.getId(id).pipe(map((data) ➜ data.map((rowId) ➜ rowId.id))
  )
);
getId(id: any) {
  return of([{ id: 1 }, { id: 2 }, { id: 3 }]);
}

In your HTML file, make sure to use the async pipe for subscription. Use the concatMap pipe from the RxJS operator to sequentially call observables and assign values to your newIds variable.

<pre>
  {{ newIds | async }}
</pre>

You can see a live demo of this in action by clicking on this link: Stackblitz Link

Answer 8

If you want to achieve this functionality, follow the steps below:

In your component file, add the following code snippet:

newIds: Observable<any> ➜ of(this.id).pipe(
  concatMap((id) ➜
    this.getId(id).pipe(map((data) ➜ data.map((rowId) ➜ rowId.id))
  )
);
getId(id: any) {
  return of([{ id: 1 }, { id: 2 }, { id: 3 }]);
}

In your HTML file, make sure to use the async pipe for subscription. Use the concatMap pipe from the RxJS operator to sequentially call observables and assign values to your newIds variable.

<pre>
  {{ newIds | async }}
</pre>

You can see a live demo of this in action by clicking on this link: Stackblitz Link

Answer 9

Answer №5

If I were to tackle this problem, I would take a different approach: for value remapping, consider utilizing the map operator:


 this.repository.getById(Ids)
  .pipe(map(response) => response.map(id => id))
  .subscribe((id) => {
      console.log(response);
      this.newIds = id;
  });

It's puzzling as to why you would need to map a value that is already present, but implementing this solution should bring clarity.

Answer 10

If I were to tackle this problem, I would take a different approach: for value remapping, consider utilizing the map operator:


 this.repository.getById(Ids)
  .pipe(map(response) => response.map(id => id))
  .subscribe((id) => {
      console.log(response);
      this.newIds = id;
  });

It's puzzling as to why you would need to map a value that is already present, but implementing this solution should bring clarity.

Waiting for the response to come by subscribing in Angular

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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